1. Field of the Invention
The invention relates to a radio transmission method for a mobile radio system, wherein a radio link is established between a central station and a mobile station by means of at least two base stations each including a transmitter and a receiver and each exchanging low frequency signals with the central station.
2. Description of the Prior Art
Such a radio transmission method is known, for example, as common-channel radio operation from the printed document German Auslegeschrift No. 1,230,471. In this document, the base station transmitters are operated with carrier frequencies which are located in the same channel and which differ in adjacent base stations by a slight carrier frequency offset and are modulated synchronously with the low-frequency signals coming from the central station. The base stations are here arranged in such a way that their service areas overlap and together cover a predetermined area within the range of which a radio link can be established between the central station and a mobile station.
Although such genuine common-frequency radio communication only requires a single carrier frequency to cover a greater service area, disturbances in the radio link will occur in the boundary zones between adjacent service areas because of interference effects. Such disturbances can be reduced to a tolerable degree only by means of considerable additional synchronization effort with regard to synchronisation by providing phase delay equilization and frequency stability in the base stations. In addition, the simultaneous operation of all base stations leads to an unnecessarily high consumption of energy which can be undesirable in cases in which only a power supply with limited output is available for operational reasons.